It is well known that victims of a heart attack should receive immediate aid in the form of cardiopulmonary resuscitation following an attack. The time delay from the moment of an attack to the initiation of CPR by a rescuer and the effectiveness of the CPR greatly influences the chance of survival of the victim. In an emergency, in addition to minimizing the delay for initiating treatment, it is equally important that the CPR received is highly effective, requiring the minimum of operator input to ensure effectiveness. Research has demonstrated that the effectiveness of the CPR is improved when chest compression is performed simultaneously with lung ventilation in addition to asynchronous lung ventilation cycles between a selected number of compression cycles. It has also been shown that increased thorax pressure, and not the heart pumping action during chest compression, causes valves in the jugular veins to open and pass blood through. These valves close during decompression. While there are devices available that can deliver chest compression that are coupled with ventilation, these systems are highly complex requiring a high level of operator skill to optimize performance parameters. Serious injury to the patient can be the result of improperly set parameters including fracture of the sternum or lung rupture if too much pressure is applied.
As well, victims of heart attacks are not limited to a particular body size or weight. The victim of a heart attack can range in weight and size from that of a small child to that of a large and possibly overweight adult. The CPR required by different sized victims therefore varies. For example, smaller victims, with a smaller chest require a lower compression force, lower compression displacement and lower ventilation volumes and pressures. Similarly, those victims with a larger chest size require a higher compression force, a higher compression displacement and higher ventilation volumes and pressures.
U.S. Pat. No. 4,397,306 discloses an integrated, non-portable, system for cardiopulmonary resuscitation and circulation support. This device comprises a chest compression means in conjunction with a lung ventilation means capable of providing high pressure ventilation synchronously with chest compression, a low pressure ventilation means for inflating the lungs at low pressure between a selected number of compression cycles and a negative pressure ventilator for deflating the lungs between chest compressions. The device is further comprised of a valve means for operating one of the ventilators, a means for restricting the abdomen to exert pressure thereon and a control means for selectively operating the chest compression means, the ventilating means, the valve means and abdomen restricting means in a selected sequence and for selected durations.
The control of this device is highly complex, requiring a high degree of operator skill to control in order to ensure optimization of input and output parameters and, hence, patient parameters that indicate recovery. Furthermore, this device does not describe a means of effectively adjusting parameters of the device to provide effective and safe CPR to patients of different sizes.
U.S. Pat. No. 4,424,806 discloses an automated ventilation, cardiopulmonary resuscitation and circulatory assistance apparatus. This device includes an airway apparatus, a vest including an inflatable bladder for compressing chest and abdominal restrainer including an inflatable bladder. An airway, vest and abdominal pneumatic control apparatus to alternately inflate and deflate the patient lungs, the vest bladder and the abdominal restrain bladder, respectively. The device has a provision for selectively adjusting the volume of gas that is coupled to the patient's lungs, and the maximum pressure that are obtained in the vest bladder and the abdominal restraint bladder. An electronic control means which allow selection of operation mode and control lung vest bladder and abdominal restrain bladder inflation and deflation by controlling respective time signals.
The control of the device is complex and requires from the operator good knowledge of human physiology to properly adjust the pressure-volume control ventilation means for delivery of simultaneously ventilation with chest compression and inflation of bladders for chest compression and abdominal restrain. Incorrect adjustment of any of these parameters, malfunction of the control system or component failure such as chest compressor control valve or pressure regulator occurs, high ventilation pressure would enter a patient lungs. In an absence of counteracting intrathoracic pressure, which is generated during chest compression may lead to the lungs rupture.
U.S. Pat. No. 4,326,507 discloses cardiopulmonary resuscitation device that cyclically compresses a patient's chest and simultaneously ventilates the patient's lungs to a safe limiting pressure over a period of time. This creates a pressure increase in the patient's thorax during systole that enhances blood perfusion. In addition continuous application of ventilation pressure during the diastolic portion of the compression cycle enhances blood gas exchange.
The simultaneous application of a benign limiting pressure during chest compression though enhances patient's safety but lowers the intrathorax pressure and in consequence takes away the benefits of high pressure ventilation during chest compression thus decrease the efficiency of CPR procedure.
Canadian Patent 979,767 discloses a self-contained resuscitation device that can provide cardiac massage with artificial respiration to a patient. The device provides a manually adjustable chest compression means and asynchronous ventilating means. The device does not disclose a means for adjusting ventilation and ventilation during compression volumes, thumping stroke and thumping force simultaneously with adjusting the span adjustment (distance between the thumper and base to accommodate a patient's chest) .
Other related patents include Canadian Patent 739,228 disclosing a heart massage apparatus with compressed gas actuating means, Canadian Patent 766,539 disclosing an external heart massage apparatus, Canadian apparatus 775,366 disclosing an external cardiac massage apparatus, U.S. Pat. No. 3,425,409 disclosing an external cardiac massage apparatus with asynchronous ventilation, U.S. Pat. No. 4,297,999 disclosing a portable resuscitation apparatus to be used in conjunction with manual external cardiac massage, U.S. Pat. No. 4,338,924 disclosing a CPR device that provides ventilation from conventional compressed gas cylinders, U.S. Pat. No. 4,702,231 discloses a portable heart massage apparatus driven by electrical motor. The motor is used to actuate a pair of hydraulic cylinders connected together in a "slave" arrangement. The "slave" cylinder is mounted on a platform adopted to be strapped to the chest of the victim, with the slave cylinder having a ram that pushes rhythmically against the sternum to squeeze the heart.
With pneumatic, volume driven chest compressor the compression depth is effected by a patient chest rigidity, thus may require subsequent corrections to the depth of chest compression means. This can be done only by interruption of chest compression because the adjustment mechanism is mounted on rotating speed reduction gear shaft. This apparatus does not have a ventilator but merely a provision to drive mechanical ventilator, neither describes the ability to deliver ventilation simultaneously with chest compression nor the adjustment of critical CPR parameters. Canadian Patent 1,231,873 discloses an external cardiac massage device.